Foil bearing with trailing edge key

ABSTRACT

A gas bearing within a cylinder is provided. The gas bearing comprises an anti-rotation tab sitting within a key way of the cylinder. Further, the gas bearing comprises a first foil forming an inner loop and an intermediary loop. The inner loop extends in a first direction from a first end to an intermediary portion. The intermediary loop extends from the intermediary to the anti-rotation tab.

BACKGROUND OF THE INVENTION

The present disclosure relates generally to a foil bearing with atrailing edge key, and more specifically, to a thin foil, hydrodynamicgas bearing comprising a trailing edge key to eliminate a foil fatiguefailure.

In general, thin foil, hydrostatic journal bearings are used to supporta rotating element in rotating machinery such as air cycle machines.Historically, the predominant journal loading was assumed to be static,(due to gravity or acceleration) or synchronous (1 time per shaftrotation); however, recent experience has shown that there areenvironments that impose a non-synchronous, high-cycle load on the thinfoil, hydrostatic journal bearings. The journal bearing is comprised ofseveral elements: top and intermediate foils are formed from asingle-piece, double wrap cylindrical foil supported by a corrugatedbump foil. When subjected to high levels of nonsynchronous loading, theformed key (anti-rotation) integral to the top/intermediate foil cracks(and in some cases separates). The crack initiates at a tight radius ata bottom of the formed key. The cracking is in part due to the geometryof the tight radius, which is an inherently high stress riser. Further,a forming operation necessary to fold the foil into a 180° bend exceedsan ultimate elongation of the foil itself, which leads to an orange peelcondition and a degradation in the material fatigue strength.

BRIEF DESCRIPTION OF THE INVENTION

Embodiments include a gas bearing within a cylinder is provided. The gasbearing comprises an anti-rotation tab sitting within a key way of thecylinder. Further, the gas bearing comprises a first foil forming aninner loop and an intermediary loop. The inner loop extends in a firstdirection from a first end to an intermediary portion. The intermediaryloop extends from the intermediary to the anti-rotation tab.

Additional features and advantages are realized through the techniquesof the present disclosure. Other embodiments and aspects of thedisclosure are described in detail herein. For a better understanding ofthe disclosure with the advantages and the features, refer to thedescription and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter that is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 illustrates a perspective view of a cylinder that houses a gasbearing, which supports a rotating shaft, according to an embodiment ofthe present invention;

FIG. 2 illustrates an example of the gas bearing intersecting a key wayof the cylinder according to an embodiment of the present invention;

FIG. 3 illustrates another example of the gas bearing intersecting a keyway of the cylinder via a trailing edge key according to an embodimentof the present invention; and

FIG. 4 illustrates another example of the gas bearing intersecting a keyway of the cylinder via a split key according to an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments described herein relate to a foil bearing with a trailingedge key, and more specifically, to a thin foil, hydrodynamic gasbearing comprising a trailing edge key to reduce or eliminate anon-synchronous or reverse on the thin foil, hydrodynamic gas bearing.An example application of the foil bearing is employing the foil bearingin an air cycle machine in an aerospace environment.

Turning now to FIG. 1, a perspective view 100 of a cylinder 110 thathouses within an inner surface 110A a thin foil, hydrodynamic gas 120,which supports a rotating shaft, is shown according to an embodiment ofthe present invention. Note that the rotating shaft is omitted forclarity in this view.

In general, the thin foil, hydrodynamic gas 120 can be a component ofrotating machinery such as an air cycle machine that sits within thecylinder 110 supporting a rotating shaft. The thin foil, hydrodynamicgas bearing comprises a foil and an air film. The foil is a staticportion of the thin foil, hydrodynamic gas bearing 120 that does notrotate and sits within a key way. The air film supports the rotatingshaft (i.e., the rotating shaft rides on the air film).

Further, the foil is positioned via a key within the cylinder withrespect to the key way (e.g., a thin sleeve, slot, or grove down thelength of the cylinder). The intersection of the key and the key wayprevents the foils from rotating, moving, sliding, etc. Embodiments ofthis intersection will be shown with respect to FIGS. 2 and 3, whichshow a magnified view 130 of FIG. 1.

FIG. 2 illustrates an example of a portion of a double wrap foil 220that intersects the cylinder 110 according to an embodiment of thepresent invention. The double wrap foil 220 is a one-piece foil thatencircles the cylinder 110 twice. That is, the double wrap foil 220extends from a first end 220A in a counter-clockwise fashion (Note:counter-clockwise is the direction of shaft rotation) along the innersurface 110A (or along the shaft omitted for clarity in this view) to anintermediate portion 220B. Continuing after the intermediate portion220B, a key 220C is formed via a 180° bend. The key 220C is a singleanti-rotation tab that sits within the key way 225. The double wrap foil220, after the key 220C, continues in the counterclockwise fashion to asecond end 220D. Note a corrugated foil 230A is included between theinner surface 130 and the intermediate portion 220B. The 180° bend,according to recent experience, has shown that in some environments anon-synchronous, high-cycle load is imposed. This load has led toanti-rotation cracking (and in some cases separating) of the double wrapfoil 220 initiated at or near the key 220C.

In view of the load issues with the double wrap foil 220, FIG. 3illustrates another example of a gas bearing intersecting a cylinder viaa trailing edge key embodiment. The trailing edge key embodiment is aone-piece foil 320 that encircles the cylinder 110 twice. As seen inFIG. 3, the foil 320 extends from a first end 320A in acounter-clockwise (e.g., direction of shaft rotation) fashion to form afirst loop within the inner surface 110A. The first loop concludes at anintermediate portion 320B. The intermediate portion 320B includes adogleg bend that directs the foil 320 under the first end 320A. Then,the foil 320 continues to form a second loop between the first loop andthe inner surface 110A. At the conclusion of the second loop, the foil320 forms a trailing edge key 320D that abuts a side of the key way 225opposite of the corrugated foil 230A.

The trailing edge key 320D is an anti-rotation tab that sits within thekey way 225. The trailing edge key 320D has a large radius 320E (i.e.,in contrast to the 180° bend of the key 220C) that significantly reducesor eliminates stress riser associated with the key 220C. The trailingedge key 320D can be formed without exceeding ultimate elongation of thefoil 320. Thus, the trailing edge key 320D eliminates the 180° bend ofthe double wrap foil 220 (e.g., replaces it with key on the trailingedge of the second loop or intermediate foil).

Turning now to FIG. 4, another example of a gas bearing addressing loadissues with the double wrap foil 220 is shown. In FIG. 4, a split key400 embodiment is illustrated via a first foil 420 and a second foil 430(e.g., respectively a top foil and an intermediate foil). The split key400 is an anti-rotation tab configuration that sits within the key way225 as further described below.

The first foil 420 extends from a first end 420A in a counter clockwisefashion to form a first loop within the inner surface 110A. The firstloop concludes at an intermediate portion 420B before turning into thekey way 225 and forming a first side 400A of the split key 400.

The second foil 430 extends from a second end 430A in a clockwisefashion to form a second loop between the inner surface 110A and thefirst foil 420. The second loop concludes by turning into the key way225 and forming a second side 400B of the split key 400.

The second side 400B of the split key 400 abuts an side of the key way225 opposite of the corrugated foil 230A, while the first side 400A ofthe split key 400 resides between the second side 400B and thecorrugated foil 230A.

The first foil 420 and a second foil 430 eliminate the double wrap foil220; thereby replacing the key 220C formed via the 180° bend with thefirst and second sides 400A, 400B of the split key 400. That is, thesingle anti-rotation tab (and its 180° bend) is replaced with twoseparate tabs for the now separate top foil and intermediate foil. Bothof the first and second sides 400A, 400B are formed with large radii420C, 430C, which have a lower stress riser than the tight 180° bend ofthe double wrap foil 220. Additionally, the larger radius of each tabcan be formed with exceeding the foil ultimate strength and sufferingthe associated degradation in material fatigue strength.

The technical effects and benefits of embodiments of the presentinvention include creating a foil bearing that is tolerant ofnon-synchronous or reverse loading and further that comprises ameasurably high load capacity. This foil bearing can be utilized inapplications with either a high external vibration environment (such ashelicopters or engine mounted equipment) or with equipment thatexperience intermittent reverse rotation (such as permanent magnetelectric motors).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of onemore other features, integers, steps, operations, element components,and/or groups thereof.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention.

Additionally, while various embodiments of the invention have beendescribed, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

1. A gas bearing within a cylinder, comprising: an anti-rotation tabsitting within a key way of the cylinder; and a first foil forming aninner loop and an intermediary loop, wherein the inner loop extends in afirst direction from a first end to an intermediary portion; and whereinthe intermediary loop extends from the intermediary portion to theanti-rotation tab.
 2. The gas bearing of claim 1, wherein theanti-rotation tab is a trailing edge key.
 3. The gas bearing of claim 1,wherein the inner loop is within an inner surface of the cylinder. 4.The gas bearing of claim 3, wherein the an intermediary foil is betweenthe inner loop and the inner surface of the cylinder.
 5. The gas bearingof claim 1, wherein the anti-rotation tab abuts a side of the key way.6. The gas bearing of claim 5, wherein the anti-rotation tab residesbetween the side of the key way and a corrugated foil within thecylinder.
 7. The gas bearing of claim 1, wherein the intermediateportion includes a dogleg bend that directs the intermediary loopbetween the inner loop and the inner surface of the cylinder.
 8. The gasbearing of claim 1, wherein the intermediary loop extends along a radiusto the anti-rotation tab.
 9. An air cycle machine comprising the gasbearing of claim 1.